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                [HAOI2012]容易题(easy)                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
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                                <h3>题目描述</h3><p><p><span style="font-size: medium"><br />
为了使得大家高兴，小Q特意出个自认为的简单题（easy）来满足大家，这道简单题是描述如下：<br />
有一个数列A已知对于所有的A[i]都是1~n的自然数，并且知道对于一些A[i]不能取哪些值，我们定义一个数列的积为该数列所有元素的乘积，要求你求出所有可能的数列的积的和 mod 1000000007的值，是不是很简单呢？呵呵！<br />
</span></p></p><hr/><h3>输入格式</h3><p><p><br />
<font size="4">第一行三个整数n,m,k分别表示数列元素的取值范围，数列元素个数，以及已知的限制条数。<br />
接下来k行，每行两个正整数x,y表示A[x]的值不能是y。<br />
</font></p></p><hr/><h3>输出格式</h3><p><p><font size="4">一行一个整数表示所有可能的数列的积的和对1000000007取模后的结果。如果一个合法的数列都没有，答案输出0。<br />
</font></p></p><hr/><h3>样例输入</h3><pre>3 4 5
1 1
1 1
2 2
2 3
4 3
</pre><hr/><h3>样例输出</h3><pre>90
样例解释
A[1]不能取1
A[2]不能去2、3
A[4]不能取3
所以可能的数列有以下12种
数列      积
2 1 1 1     2
2 1 1 2     4
2 1 2 1     4
2 1 2 2     8
2 1 3 1     6
2 1 3 2     12
3 1 1 1     3
3 1 1 2     6
3 1 2 1     6
3 1 2 2     12
3 1 3 1     9
3 1 3 2     18
</pre><hr/><h3>提示</h3><p><p>数据范围<br />
30%的数据n&lt;=4,m&lt;=10,k&lt;=10<br />
另有20%的数据k=0<br />
70%的数据n&lt;=1000,m&lt;=1000,k&lt;=1000<br />
100%的数据 n&lt;=109,m&lt;=109,k&lt;=105,1&lt;=y&lt;=n,1&lt;=x&lt;=m<br />
</p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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